1. Field
Embodiments of the present invention relate to improvements in the vehicle frame structure of a vehicle, such as an all terrain vehicle.
2. Description of the Related Art
All terrain vehicles often employ a body frame formed by assembling pipes or plates in a tower-like form.
As illustrated in FIG. 1 of Japanese Patent Laid-Open No. Sho 60-255593, a main pipe extends from a head pipe in a longitudinal direction of a vehicle. Seat pillar tubes extend from a longitudinally intermediate portion of the main pipe. Down tubes extend downward from the head pipe and then toward the rear of the vehicle. An engine is supported by the down tubes and the seat pillar tubes.
As illustrated in FIG. 2 of Japanese Patent Laid-Open No. Sho 60-255593, the down tubes are composed of two left and right tubes. Also the seat pillar tubes are composed of two left and right tubes. A body frame is assembled in a tower-like form. The main pipe extends from the head pipe in such a form as to cross immediately above the engine.
In FIG. 1 of Japanese Patent Laid-Open No. Sho 60-255593, the engine is mounted on the body frame by being shifted in the left-right direction of the vehicle body in an assembly plant. After the vehicle has been delivered to a user, the engine undergoes inspection and maintenance, and repair while remaining mounted on the body frame.
The engine is composed of a crankcase, a cylinder extending upward from the crankcase, a cylinder head allowed to overlap the cylinder, and a cylinder head cover put on the cylinder head. As illustrated in FIG. 1 of Japanese Patent Laid-Open No. Sho 60-255593, the uppermost cylinder head cover is close to the main pipe.
A valve train mechanism (a rocker arm, a camshaft, a valve stem, etc.) is disposed inside the cylinder head cover. Because of its complicated structure, the valve train mechanism needs to undergo inspection and maintenance. To remove the cylinder head cover from the cylinder head, it is necessary to ensure a sufficiently large clearance between the cylinder head cover and the main pipe.
Further, considering the replacement of a piston ring, it is desirable that the cylinder head and the cylinder (the cylinder block) be removed from the crankcase. To do so, it is necessary to further increase the sufficiently large clearance between the cylinder head cover and the main pipe. However, if the clearance is enlarged as mentioned above, it is necessary to further raise the main pipe, with the result that the body frame is enlarged.
Amid the demand for the downsizing and weight reduction of vehicles, the enlargement of the body frame is not preferable. Therefore, a technology is required that can downsize the body frame of a vehicle whose main pipe is disposed immediately above an engine.